Recent experiments in this laboratory have revealed an unusual and unexpected type of metabolic compartmentation of central metabolic pathways in mitochondria from several tumor cell lines, which does not appear to occur in those from normal cells. Two different and independent pathways of malate oxidation have been found: one acting only on internally-generated malate, the other only on malate imported from the medium. This proposal is concerned with biochemical elucidation of the mechanisms of "preferred access" of malate and their relationships to the oxidation of glutamine, the major respiratory fuel of tumor cells, and to the generation of a number of products (citrate, aspartate, alanine, pyruvate) required in cytosolic biosynthesis in tumors. The further purification of tumor mitochondrial malic enzyme and malate dehydrogenase, their kinetics and allosteric regulation, and their possible occurrence in the form of multienzyme clusters are to be investigated to provide an explanation for the compartmentation observed. Similarly, the activity and regulation of the relevant membrane transport system will be examined. The production of acetoin, a heretofore undescribed product of pyruvate oxidation in tumor mitochondria, will also be examined. (E)